1. Field of the Invention
The present invention relates to a method and weaving machine for producing a multi-axial fabric comprising a triaxial fabric having two sets of obliquely arranged warp yarns of different direction and a set of weft yarns, which are interwoven, and a set of warp yarns which are transverse to the weft yarns and which are interwoven to the weft yarns of the triaxial fabric.
Definition:
The term "oblique warp yarns" means warp yarns which, after being woven to a fabric, run along a direction which is oblique with respect to a weft-wise direction.
The term "straight warp yarns" means warp yarns which, after woven to a fabric, run along a direction which is transverse to the weft-wise direction.
2. Description of Related Art
A triaxial fabric is known in, for example, U.S. Pat. No. 4,438,173 by Wayne. In this basic type of a triaxial fabric, two sets of oblique warp yarns are interwoven with a set of weft yarns. In order to obtain such triaxial fabric, a weaving machine is proposed, where a pair of opposite, spaced arrays of heddles are provided for supporting two sets of oblique warp yarns. The heddles are alternately arranged between the opposite arrays and are subjected to reciprocal movement so that the heddle between the opposite arrays are crossed with each other, which causes a shed to be created to which a weft yarn is introduced, to which a beating movement by a beater is applied to create a cloth fell. Furthermore, a mechanism is provided for obtaining an endless, alternate, opposite, weft-wise, stepwise movement of the opposed arrays of heddles every time after the execution of the beating movement, so that, after being interwoven to the weft yarns, the oblique warp yarns are arranged oblique to the weft direction.
Known from Japanese Unexamined Patent Publication (Kokai) No. 63-92751 is a weaving machine which includes a pair of delivery rolls defining thereon helical grooves for displacing two sets of oblique warp yarns (upper oblique warp yarns and lower oblique warp yarns) oppositely along the weft direction, a guide roll arranged on one side of the delivery rolls adjacent the cloth fell for guiding another set of straight warp yarns, and push type-heddles of a fork shape for obtaining a downward movement of the upper oblique warp yarns for creating a shed so that the upper, oblique warp yarns are interwoven with the lower weft yarns, and so that the lower oblique warp yarns and the straight warp yarns are sandwiched between the upper, oblique warp yarns and the lower weft yarns.
The Japanese Unexamined Patent Publication No. 1-292140 discloses a weaving machine which comprises two sets of horizontal, opposite, spaced arrays of heddles, for guiding two sets of arrays of oblique warp yarns, and elongated rocking heddle levers for supplying straight warp yarns at locations inwardly of the arrays of the oblique warp yarns. The heddle levers effect their designated movement at the area inwardly of the arrays of the oblique warp yarns so that the straight warp yarns are interwoven to a fabric from the inner side of the oblique warp yarns.
The Japanese Unexamined Patent Publication No. 2-6649 discloses a weaving machine which has loops of guide chains on which heddle guide needles for oblique warp yarns are vertically movably supported. The guide chain rotates about vertical axes for obtaining stepwise, weft-wise movement of the oblique warp yarns as is necessary to obtain usual triaxial fabric as illustrated in U.S. Pat. No. 4,438,173. Furthermore, on one side of the arrays of the guide needles, away from the cloth fell, transverse arrays of heddle guide needles for straight warp yarns are provided. These needles are subjected to a designated shedding movement so that the straight warp yarns are interwoven to a weft yarn.
Furthermore, in the Japanese Examined Utility Model Publication No. 56-42380, a weaving machine is provided, where upper and lower heddles of a pushing type for straight warp yarns are used for obtaining simultaneous movement of the straight warp yarns and one of the sets of the oblique warp yarns to create a shed into which the weft yarn is inserted. Namely, straight warp yarns are arranged is parallel, while two sets of oblique warp yarns are shedded, so that a weft yarn is inserted to the shed on one side of the straight warp yarns. As a result, a fabric is obtained where the straight warp yarns are located between the oblique warp yarns and a weft yarn. In this patent, the heddles can only move the one set of the oblique warp yarns.
Finally, Japanese Patent Publication No. 58-163750 discloses a multi-axial fabric comprising oblique warp yarns of different direction and straight warp yarns.
In the Japanese Unexamined Patent Publication No. 63-92751, due to the employment of the fork-shaped pressing heddles which need a large transverse width for maintaining a desired action for pressing the oblique warp yarns, the spacing between adjacent oblique warp yarns must be large, which causes the fabric, as produced, to be relatively coarse. Furthermore, the construction of the fabric is such that four sets of the yarns (a set of weft yarns, two sets of oblique warp yarns and a set of straight warp yarns) are arranged in such a manner that two sets of yarns are woven while sandwiching, therebetween, the other two sets of yarns, which causes the woven structure of the yarns to be unstable, causing the fabric to be easily deformed when subjected to an outer tension. In particular, when the construction is such that the upper and lower sets of the oblique warp yarns are sandwiched between the straight warp yarns and weft yarns, the instability of the structure becomes extremely high.
The Japanese Unexamined Patent Publication No. 1-292140 is advantageous from the view-point of economy due to the fact that a conventional-type weaving machine for triaxial fabric is modified so that another set of elongated heddle levers are added. However, such an additional set of elongated heddle levers for the straight warp yarns must be provided in a very limited space inwardly of the opposite arrays of the heddle for the oblique warp yarns. This causes the device to be complicated, on one hand, and the cost to be increased, on the other hand. Furthermore, straight warp yarns must be done by moving the elongated heddle levers via spaces between adjacent oblique warp yarns. Thus, there is a lower limit in the spacing between the adjacent oblique warp yarns, causing the fabric to become coarse. The produced fabric has a construction that the straight warp yarns are arranged between the two sets of oblique warp yarns of different directions. Namely, the straight warp yarns are interwoven to the weft yarns from the inner side, which causes the fabric to become unstable, due to the fact that the spacing between adjacent straight warp yarns can easily be changed, on one hand, and makes the weaving machine to be of a complicated structure, on the other hand.
In the Japanese Unexamined Patent Publication No. 2-6649, the shedding movement of the oblique warp yarns is done by the oblique warp yarn guide needles which are mounted on the guide chain, which causes the fabric to become coarse. Furthermore, the oblique warp yarns and the straight warp yarns are merely selectively interwoven, causing instability of the woven structure. Namely, only one weft yarn among four weft yarns constructing one repeat unit is interwoven with the oblique warp yarns, which makes the fabric unstable. In other words, the oblique warp yarns are interwoven to the weft yarn only at limited portions where the oblique warp yarns cross each other.
In Japanese Examined Utility Model Publication No. 56-42380, one set of the oblique warp yarns moves to together with the straight warp yarns. Thus, at the points where the oblique warp yarns of different directions are crossed with each other due to the fact that the heddles can move only one set of the oblique yarns, the straight warp yarns cannot always be interwoven with the weft yarns, causing the fabric as produced to be unstable.
In the Japanese Unexamined Patent Publication No. 58-163750, among all the points where the oblique warp yarns are interwoven with the weft yarns, some points lack in the provision of the straight warp yarns, which makes the fabric unstable.